In this paper，the effects of the oxidizer particle size on the aging behaviour of HTPB propellants have been studied. The experiments are done in air at 90℃. The aging behaviour is estimated by means of the changes in mechanical properties，hardness，weight loss and changes in burning rate of HTPB propellants. Also，the DSC is relerred to. The results of these experiments show that，in HTPB propellants，the reduction of the oxidizer particle size facilitates the increase of the aging behaviour of HTPB propellants. The DSC of the oxidizer particle size has further comfirmed the conclusion.